The Portland daily press., 1887-04-23

cause of the accident. This brings up a
phase Of railroad and bridge accidents which
Is at present receiving great deal OF atten-
ton. Capitalization In the material OF iron
bridges Is an element OF danger now so well
recognized that the Pennsylvania Railroad
Company has adopted the definite policy OF
substituting stone for iron bridges, and the
same plan Is being followed by other rail-
load companies.
The lifetime Of an iron bridge Is from
twenty to twenty-five years, and constant
care Is necessary to insure Its safety. The
Ashtabula bridge was thirteen years old,
and at the time 1t fell beneath the weight OF
two engines and heavy express train the
theory was commonly advanced that crystal
llzatiOn had impaired its original strength
The two great moving causes OF crystalliza-
ton are vibration and the hammer blows Of
the locomotive which gradually, by repeated
impact, turn the fiber OF iron OF steel into q
mass Of crystals, needing only some unusual
pressure or blow to cause them to break
apart. Add 10 this the oscillation caused by
the passage OF trains at high rate Of speed,
and it win be seen that an iron bridge Is ex-
posed 10 peculiar perlls, which can only be
slant renewals.
Capitalization was one OF several theories
advanced by Park Benjamin, a New York en-
gineer, 70 account for the Tay bridge acci-
dent He said:
General indications 20 to show that the
cause must be sought in an abnormal CON
dition Of the structure, or rather one which
did not enter into the calculations OF the
builders. such condition. would be the de-
terioration Of the metal by its change from
a fibrous to crystalline state under repeated
vibration. That this occurs in railway
bridges has been vigorously disputed by
many well-kn0wn engineers. On the other
hand, many examples are quoted by differ
ent authorities to support the theory. Apro-
pos to this particular accident, distinguish
ed French engineer and iron founder, now In
this country informs us that he has known
bars Of iron made by himself from Scotch
pig to change from tough fbrous to a brit
tie crystalline structure In travelling by rail
only from the North Of France to Paris.
This Is. Of course, an extreme instance.
again. recent research has demonstrated
qulescent load that fact is little proof Of sta
bility under repeated shocks and vibrations.
Metals are believed to have q life A bar,
for example. may stand million vibrations
and break down at the million and first, and
yet the last shock may be lighter than pre-
ceding ones. Attempts, however, to reduce
this law to practical application have elected
an abundance Of conflicting evidence, but,
nevertheless, 1t Is well settled that In no de-
partment OF mechanics Is an extended course
Of actual experimenting more urgently need
ed or Of grayer public Importance"
The strength OF the Tay bridge at the time
OF its building was such that II was pro
nouneed perhaps the most remarkable
structure IN the world. Engineering,
British magazine, speaking Of its test. when
five engines, weighing $50 tons, were placed
on a single span, said: ''The result Is the
complete establishment Of this fact $50 Inn
portant to the public that the bridge Is
strong out Of all proportion TO its possible
necessities. The load which the structure Is
calculated TO carryls six times greater than
that to which 1t was subjected
And yet this great bridge, which cost ST.
10000, collapsed within few months after
II was finished, the accident being the only
one in all railroad history In which no sur
vivor lived to tell the tale.
The theory Of capitalization put forward at
the time Of the Ashtabula bridge disaster Is
now accepted as accounting for many railroad
accidents, and seems peculiarly applicable 10
the fall Of the Bussey bridge. Vibrations
and hammer blows would seem TO have crys-
tallized some portion Of the structure and
prepared 1t for fall when at last the "llfe"
Of girder had been exhausted, and 1t broke
beneath the engines humping driving
wheels.